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Measurement Techniques
Published in Marvin C. Ziskin, Peter A. Lewin, Ultrasonic Exposimetry, 2020
Marvin C. Ziskin, Peter A. Lewin
The efficiency of the interferometric procedure is demonstrated in three examples. In the first, a multielement linear transducer array with dynamic focusing and sector scanning is investigated. Generally speaking, the requirements for the spatial resolution of the measuring system are particularly high in the focal range of these transducers. Figure 7 shows a typical pulse generated by a linear array. In Figure 8, the peak value of the particle displacement is represented in terms of the position in the focal plane. In the upper part of the figure, the direction of radiation is 0°, i.e., normal to the transducer surface. The half width amounts to about 1 mm, (here, three ultrasonic wavelengths). In the lower part of the figure, the transducer radiates at 40° to the normal. Here, due to reduced coherence the half width is somewhat larger and the corresponding peak value of the particle displacement is less.
All About Wave Equations
Published in Bahman Zohuri, Patrick J. McDaniel, Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Bahman Zohuri, Patrick J. McDaniel
Interferometry is a family of techniques in which waves, usually electromagnetic waves, are superimposed causing the phenomenon of interference in order to extract information. Interferometry is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy (and its applications to chemistry), quantum mechanics, nuclear and particle physics, plasma physics, remote sensing, biomolecular interactions, surface profiling, microfluidics, mechanical stress/strain measurement, velocimetry, and optometry.
X-Ray Dark-Field Imaging of Lung Cancer in Mice
Published in Ayman El-Baz, Jasjit S. Suri, Lung Imaging and CADx, 2019
Deniz A. Bölükbas, Darcy E. Wagner
Interferometric methods vary in their experimental setups, illuminating radiation requirements, and their signal acquisition. A common feature, though, is that these techniques require a highly parallel and monochromatic X-ray beam source with restricted spatial and temporal coherence lengths [39, 49, 50]. Due to the technical challenges associated with implementing X-ray beam sources with such parameters, routine use of these X-ray imaging modalities in the clinics or industry has been limited. In 2005, Weitkamp et al. [51] first demonstrated that two gratings can be used for differential phase-contrast imaging from polychromatic X-rays of brilliant synchrotron sources. Following this in 2006, Pfeiffer et al. [39] showed an alternative approach to retrieve quantitative phase images with polychromatic X-ray sources of low brilliance and dark-field scatter images using conventional X-ray tube sources [47] by exploiting the Talbot-Lau interferometer. His team proved that addition of a third grating to the system resulted in successful adaptation of this technique to X-ray sources of low brilliance [39]. Using a source grating G0, a phase grating G1, and an analyzer absorption grating G2 (Figure 4.5), they were able to achieve dark-field scatter images of high quality. This major achievement allowed for acquisition of adequate X-rays with conventional polychromatic laboratory sources and led to a more frequent use of grating-based imaging in preclinical models for biomedical applications [48].
Contact force sensors in minimally invasive catheters: current and future applications
Published in Expert Review of Medical Devices, 2021
Weyland Cheng, Manye Yao, Bo Zhai, Penggao Wang
A well-known commercial fiber optic CF catheter is the TactiCath™ Quartz catheter (Abbott, Chicago, IL, USA), which incorporates a Fabry-Pérot cavity. Fabry-Pérot interferometry uses multiple-beam interference where phase differences between reflected and transmitted light beams alter according to the distance between two parallel semi-reflective surfaces in the cavity. Multiple reflecting beams interact, producing fringes that vary in intensity based on the distance between the two reflective surfaces. The reflected optical power (Pr) can be expressed as a function of the incident optical power (Pi), the reflectivity of the two surfaces (R1 and R2), and the phase shift (φ) from one reflective surface to the other (see Figure 2).[28]:
Manual interferometric device for routine non-invasive tear film break-up time assessment
Published in Seminars in Ophthalmology, 2021
Sania Vidas Pauk, Igor Petriček, Martina Tomić, Tomislav Bulum, Sonja Jandroković, Miro Kalauz, Sanja Masnec, Tomislav Jukić
The lipid layer, lit by white light, appears in colored fringes that occur from interference between light reflected from the lipid layer’s surface and form the interface between that layer and the tear film’s aqueous layer. The method is called interferometry. Semiquantitative interferometry, introduced by Norn in 1979, was performed by placing the small opaque glass in the slit lamplight.27 However, the corneal lipid layer area’s size visualized this way is quite insufficient for adequate assessment of the lipid layer. While commonly used to assess tear lipid layer thickness, interferometry can also be used to measure NIBUT, the time between the last blink and the appearance of the first lipid layer discontinuity.28 Over time, many instruments and prototypes of interferometer have been developed, and the most used for lipid layer analysis and NIBUT measurement was Keeler Tearscope presented by Guillon JP.15,29
Peripheral eye length measurement techniques: a review
Published in Clinical and Experimental Optometry, 2020
Ingrid Ornella Koumbo mekountchou, Fabian Conrad, Padmaja Sankaridurg, Klaus Ehrmann
The first reported measurement of peripheral EL using partial coherence interferometry was by Fercher et al. where they obtained the fundus profile by measuring in steps of 2° from 24° nasal to 22° temporal along the horizontal meridian.1991 At that time, partial coherence interferometry was found to have several advantages compared to A‐scan ultrasonography such as greater longitudinal accuracy and transverse resolution, as well as improved patient comfort and acceptance due to the non‐contact method. Other advantages include the need for only one interferometric measurement to identify path length matching and the insensitivity to small eye movements. However, disadvantages of this technology are its complex interferogram, limited speed and sensitivity of the dual‐beam, the need for additional components, and lower sensitivity.2016 The other drawbacks are that light is strongly attenuated by opaque ocular media, and there are fixation problems that can hinder the measurements.2002 Moreover, the method requires that the experimenter be skilled in checking interference fringes.1993 In addition, measurements with this setup are time‐consuming (the patient needed to look into the ‘laser’ beam the entire time and it took about 15-minutes for one measurement for a skilled operator). Hence, this method was found less applicable for a larger number of patients, especially elderly1991 and young people.